with a national security bomb shell. The government fought back against that fugitive who spilled top secrets with stern words from the president in a dramatic new claim from the nation's top intelligence officers. They revealed congress that more than 50 terror plots were stopped by the nsa secret program, phone reco e-mails and internet traffic. In a success story forcefully delivered as memories of 9/11 filled the hearing room. Brian ross starts us off Reporter: The target of the al queda plot revealed today was the new york stock exchange, the symbol of america's financial power. We found, through electronic surveillance, that they were actually in the initial stages of plotting to bomb the new york stock exchange. Reporter: In testimony before a mostly supportive committee of congress, the fbi's number two, sean joyce, said tapping into the email of an al qaeda leader in yemen led then to this man in kansas city and then two other americans prepared to attack in 2008. I sit before you today, humbly, to say these tools have helped us. Reporter: Of the three men conducted surveillance on the heavily guarded stock exchange and wrote, in an email to yemen, intercepted by the government, "i have visited the tourist locations you asked me about." But the plot never developed any further. The fbi disrupted and arrested these individuals. Reporter: The officials said more than 50 terror plots have been disrupted worldwide by the controversial programs, ten of them in the u.S., Including the new york subways. All part of the full scale press to defend the secret nsa programs. If you're a u.S. Person, then nsa is not listening to your phone calls and it's not targeting your emails unless it's getting an individualized court order. Reporter: Civil liberties groups said the government was exaggerating the importance and the safeguards of its secret surveillance programs. The question was not whether the properties were disrupted but whether we need to engage in dragnet surveillance. Reporter: There was suggests that the september 11 attacks could have been p prevented if the nsa had the secret surveillance programs then that it was forced to defend now. I would much rather be here today debating this point than trying to explain how we failed to prevent another 9/11. Reporter: Keith alexander revealed that edward snowden was able to get his hands on so many top secret documents because he was trained as an analyst and was given classified information, keys to the kingdom. No idea where he is. Still hiding in hong kong. News of the foiled plot

This transcript has been automatically generated and may not be 100% accurate.